From the German Patent DE-PS No. 33 42 038 an indicia-evaluating apparatus is known which includes a reader provided with a reading head and an evaluating or analyzing logic.
Passing past the reading head is a carrier in form of a web and containing at least one identification field with markings defining the identification. These markings or indicia are holes punched into the web and are recognized by the reading head by detection of the light transmitted through the holes.
This system is disadvantageous because irregularities, defects, disturbances and the like along the surface of the web or damages of the web itself, like holes or ruptures, are recognized as markings and thus result in incorrect readings.
To avoid these problems, the reader is operatively connected to a detector for an activating mark which precedes the identification field on the web and activates via the detector an evaluating or analyzing logic only immediately before the passage of the identification field past the reading head.
Interfering signals present outside the identification fields are thus prevented from being recognized by the evaluating or analyzing logic which receives a signal sequence only during movement of the identification field past the reading head.
The activating mark is physically different from the carrier web and the respective markings so that they are not confused as identification marks even when the web is damaged or defective. Nevertheless, interfering signals were encountered, as defects or other disturbances on the web were picked up while passing with the identification field past the reading head.